1. Field of the Invention
The present invention relates to magnetically levitated (maglev) pumps. More specifically, the present invention relates to those corresponding to a cleanpump employing a magnetic bearing and used for medical equipment, such as artificial heart.
2. Description of the Background Art
FIGS. 8A and 8E, show a conventional maglev pump. More specifically, FIG. 8A is a vertical cross section thereof and FIG. 8B is a cross section taken along a line XIIIBxe2x80x94XIIIB of FIG. 8A. FIG. 9 is a cross section taken along a line IXxe2x80x94IX of FIG. 8A. FIG. 10 is a cross section taken along a line Xxe2x80x94X of FIG. 8A.
Initially, with reference to FIG. 8a through FIG. 10, a conventional maglev pump will be described. As shown in FIG. 8A, a maglev pump 1 includes a motor portion 10, a pump portion 20 and a magnetic bearing portion 30. In pump portion 20, a casing 21 accommodates a pump chamber 22 in which an impeller 23 rotates. Impeller 23 has a plurality of vanes 27 spirally provided, as shown in FIG. 8B. Casing 21 is formed of a cylindrical, non-magnetic member and impeller 23 includes a non-magnetic member 25 having a permanent magnet 24 configuring a non-controlled magnetic bearing and a soft magnetic member 26 corresponding to a rotor of a controlled magnetic bearing. Permanent magnet 24 is divided in a circumferential direction of impeller 23 and magnets adjacent to each other are magnetized to have opposite magnetic poles.
Opposite to the side of impeller 23 provided with permanent magnet 24, external to pump chamber 22 there is provided a disk rotor 12 supported by a shaft 11. Rotor 12 is rotatably driven by a motor 13. Rotor 12 is provided with the same number of permanent magnets 14 as impeller 23 that face permanent magnet 24 of impeller 23 to provide attraction. Adjacent permanent magnets 14 are magnetized to have opposite magnetic poles.
Furthermore, opposite to the side of impeller 23 provided with soft magnetic member 26, an electromagnet 31 and a position sensor (not shown) are provided in magnetic bearing portion 30. Electromagnet 31 and the position sensor allow balance with the attraction of permanent magnets 24 and 14 to hold impeller 23 at the center of pump chamber 22.
In maglev pump 1 thus configured, attraction acts between permanent magnet 14 (embedded in rotor 12 and permanent magnet 24 provided in impeller 23, axially in one direction. This attraction is exploited to provide magnetic-coupling to rotatably drive impeller 23 and obtain radial supporting-stiffness. To match it to this attraction, a flow of current is passed through a coil of C-shaped electromagnet 31, which in turn attracts impeller 23 axially in the other direction to levitate impeller 23. As rotor 12 is rotatably driven by motor 13, permanent magnets 14 and 24 provide magnetic-coupling, impeller 23 rotates and a fluid is sucked through an inlet 60 and discharged through an outlet 70 (see FIG. 8B). Impeller 23 is accommodated in casing 21 and thus isolated from rotor 12 and it is also not contaminated by electromagnet 31. Thus, maglev pump 1 delivers fluid (blood if it is used as a blood pump) held clean.
Note that as shown in FIGS. 9 and 10, a conventional maglev blood pump has electromagnet 31 with an arcuate yoke 41 and pairs of magnetic poles 42 and 43, 44 and 45, and 46 and 47 each arranged radially.
If maglev pump as shown in FIGS. 8A and 8B is used as a blood pump for an artificial heart, it is implanted in a body or used adjacent thereto. As such, it cannot be supplied with energy constantly from an external power supply. Typically, it is supplied with energy obtained from a mobile battery or a battery implanted in the body. As such, to use it for a long term, energy consumption must be minimized. Furthermore, if it is used for human body, it is required to have a small size and it also must be taken great care of to be reliable.
Conventional maglev pump 1, however, as shown in FIGS. 9 and 10, has each electromagnet with magnetic poles arranged radially. As such, the space for accommodating the coil cannot be effectively obtained. As such, magnetic bearing portion 30 must be disadvantageously increased in size to provide an additional space for the coil to reduce the power consumption of the electromagnet.
More specifically, while the power consumption of the electromagnet is reduced by increasing the winding count of the electromagnet coil or increasing the diameter of the wire of the coil, either technique requires increasing magnetic bearing portion 30 in size to ensure a large space for accommodating the coil. Furthermore, conventional maglev pump 1 has electromagnet 31 with an arcuate yoke. This makes it difficult to wind the coil and also hardly ensures insulation resistance between the coil and the yoke.
Furthermore, as shown in FIGS. 8A and 8B, maglev pump 1 has a partition corresponding to casing 21 of plastic material, ceramic material or nonmagnetic metal material provided between soft magnetic member 26 of impeller 23 in pump chamber 22 and electromagnet 31 of magnetic bearing portion 30 and between soft magnetic member 26 of impeller 23 and position sensor 32 detecting the position of impeller 23. As such, impeller 23 and electromagnet 31 are spaced far apart from each other. Thus, to levitate impeller 23 electromagnet 31 is required to pass a large amount of current. Furthermore, the sensor sensitivity also degrades as impeller 23 and position sensor 32 are spaced far apart from each other.
More specifically, if the partition is formed of plastic material, the partition is less durable and can thus not be used for a long term. If the partition is formed of metal material and position sensor 32 is a magnetic sensor, then it has eddy current generated internal thereto to result in a loss and it also degrades the sensor sensitivity as it spaces position sensor 32 apart from a target.
Therefore the present invention mainly contemplates a maglev pump capable of miniaturizing a magnetic bearing portion.
The present invention also contemplates a maglev pump capable of reducing the distance between an electromagnet and an impeller and also reducing the distance between a sensor and the impeller to reduce the electromagnet""s coil current and enhance the sensitivity of the sensor output.
The present invention generally provides a maglev pump wherein a pump portion is provided with a rotative portion internal to a casing, the rotative portion is coupled with a rotation driving portion physically out of contact therewith and it is also supported by a controlled, magnetic bearing portion physically out of contact therewith, the rotative portion is rotated by the rotation driving position to discharge fluid, a position sensor detects the position of the rotative portion in levitation and in response to the output of the position detection portion the controlled magnetic bearing portion is controlled, wherein the magnetic bearing portion is configured of a plurality of electromagnets formed of a magnetic pole, a yoke and a coil and the electromagnet has magnetic S and N poles each with at least the yoke and coil arranged circumferentially.
As such in an embodiment of the present invention a magnetic bearing includes electromagnets each having a magnetic pole and a yoke that are arranged circumferentially. This ensures a large space for winding a coil without increasing the space for the magnetic bearing portion or increasing the size of the pump. Since the coil can be accommodated in such a large space, the electromagnet coil can have an increased winding count and an increased wire diameter and consequently its power consumption can be reduced. Furthermore, the electromagnet can have a yoke in the form of a cylinder or a prism to facilitate winding a coil and thus readily ensure the insulation withstand voltage between the coil and the yoke.
More preferably, the electromagnet has a pair of magnetic poles circumferentially arranged and the electromagnet has a pair of magnetic poles radially arranged.
Still more preferably, the rotative portion is provided in a form of a disk having a side facing the rotation driving portion and provided with a permanent magnet circumferentially arranged and the rotative portion and the rotation driving portion are magnetically coupled together physically out of contact with each other, and the electromagnet has three pairs of magnetic S and N poles.
Furthermore the present invention in another aspect provides a maglev pump wherein a pump portion is provided with a rotative portion internal to a casing, the rotative portion is coupled with a rotation driving portion physically out of contact therewith and it is also supported by a controlled, magnetic bearing portion physically out of contact therewith, the rotative portion is rotated by the rotation driving portion to discharge fluid, a position sensor detects the position of the rotative portion in levitation and in response to the output of the position detection portion the controlled magnetic bearing portion is controlled, wherein the magnetic bearing portion includes a plurality of electromagnets each directly facing the rotative portion or the position detection portion includes a magnetic sensor directly facing the rotative portion.
Thus in the present invention the magnetic bearing portion can have a plurality of electromagnets directly facing a rotative portion or a magnetic sensor directly facing the rotative portion to reduce the distance between the rotative portion and the electromagnets or the magnetic sensor corresponding to a plane in which the electromagnetic force of the magnetic bearing acts. Thus, the pump can be levitated with a reduced amount of current flowing through an electromagnet coil for generating electromagnetic force to levitate the same, which is advantageous when the present pump is used as a blood pump since current consumption is one of its significant issues. Furthermore, the position sensor can be enhanced in sensitivity.
More preferably, the position detection portion includes a core formed of a soft magnetic material and a coil wound around the core.
Still more preferably, any of the electromagnet and the position detection portion is flipped to the casing by any of welding, brazing, press-fitting, pressure-welding, shrink-fitting and bonding or a combination thereof.
Still more preferably, the rotative portion is provided in the form of a disk having a side facing the rotation driving portion and having a first permanent magnet circumferentially arranged and the rotation driving portion has a second permanent magnet circumferentially arranged to face the first permanent, magnet, the first and second permanent magnets achieving magnetic-coupling to couple together the rotative portion and the rotation driving portion physically out of contact with each other, and the pump portion has an internal surface coated with heparin.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.